Cigars, cigarettes, and cigarillos (generally known as smoking articles) may be analysed for the composition of the smoke that they produce using a device known as a smoking machine. A smoking machine typically comprises at least one holder for holding a smoking article, and a puffing means for drawing air in a controlled fashion through the smoking article as it burns. The smoke drawn from the smoking article is referred to as mainstream smoke and is collected for further analysis. The smoke generated between puffs is referred to as sidestream smoke, and is usually conveyed away from the cigarette using an air extraction system. An ash tray may be provided to collect the ash produced by the smoking article as it burns.
The results obtained by analysing the composition of the mainstream smoke may be used in characterising the smoking article, or by regulators to determine the yield of smoke components and whether the smoking article is below a predefined ceiling for each component. Since the smoking article is destroyed during the process of smoking it is imperative that the process of smoking is controlled adequately and repeatably to ensure meaningful comparisons can be made between brands and against standards. Consequently the machines used are defined in part by international standards of design and construction such as ISO3308:2012 (International Standards Organisation standard “routine analytical smoking machine—definitions and standard conditions). One of the features of the smoking machine design is the control of air flow over the smoking article during smoking, and this is typically required to be of a particular magnitude.
In a common type of smoking machine where the articles to be smoked are placed side by side in a straight line (a linear smoking machine) the direction of airflow is intended to be along the smoking portion of the smoking article. However in practice the airflow may be at an angle to the axis of the smoking article. This angle may vary from article to article depending on the position within the line of smoked articles and the extraction system employed to remove the smoke. Moreover, known smoking machines may introduce some turbulence in the airflow. These effects may have an impact on the uniformity of the smoking process and on the absolute magnitude of the yield from the smoking article.
Previous attempts at controlling the flow of air over the smoking article have included providing a diffusing plate above the smoking article (commonly known as a Burgess plate), and using variable controlled air extraction. However there remain some inconsistencies in air flow between machines and also within individual machines.